Answer: The part of speech of the italicized word ("open") is adjective.
Explanation: An adjective is a word that describes a noun or pronoun by adding information about it, such as its color or size. There are different type of adjectives: some of them are qualifying adjectives and classifying adjectives. Moreover, a noun or pronoun can be modified by more than one adjective. In the sentence provided, "open" is an adjective that is premodifying and describing the noun "auditorium".
